Question

if the displacement - time graph for a particle is parallel to time axis, how much is the velocity of the particle?

Answer 1

Velocity of a particle is given by the slope of displacement-time graph.
Since it is parallel to time axis, the slope is 0.
So velocity of the particle is 0.

Answer 2

the velocity will be 0 because parallel to time -axis in a displacement time graph means distance remains same and the time is increasing and this could only be possible if the body's velocity is 0.
           i hope that this will help u.